The invention relates to a device for detecting a key which has been inserted into a lock of a motor vehicle, in particular into its ignition lock, and to a correspondingly configured key.
Keys, in particular ignition keys of motor vehicles, are nowadays increasingly equipped with electronic components which permit communication with systems disposed at the lock end, for example control units of electronic ignition systems. The electronic keys are distinguished by an increased level of protection against counterfeiting, so that unauthorized use of the system can be prevented with improved probability.
U.S. Pat. No. 5,808,372 to Schwegler et al. (German patent DE 195 39 852 C1) discloses a system in which an ignition key and a motor vehicle functional unit communicate with one another. The key is equipped with a long-range communications channel for transmitting remote-control commands and with a further, short-range communications channel via which it is in communication with an ignition-lock-end control circuit. The state in which the ignition key is inserted in the ignition lock can be sensed on the basis of a transmission of data information via the short-range communications channel. The key contains a transmitter and a receiver which are connected to a logic control circuit and are controlled thereby.
German patent DE 44 14 734 C2 discloses a circuit arrangement for sensing the switching states of motor vehicle activation means, in particular in the form of a keyless motor vehicle lock system with a transponder that is carried by the user. The circuit contains a generator which intermittently generates pulses for switching on and off a voltage supply main switch, and a microprocessor (logic control unit) for controlling various functions when an activation of the activation means is sensed.
European patent application EP 0 115 747 A1 discloses an immobilizer which can be activated by an electronic key which can be inserted into a fixed receptacle section, signals being transmitted by varying the impedance of inductors. By means of the inductive coupling between the electronic key and the fixed receptacle section it is possible to transmit both data and supply energy to the key. The vehicle-end interrogation device is continuously active and generates an output signal of constant amplitude as long as there is no key introduced into the receptacle section. If the key is inserted, there is, owing to the magnetic coupling, a change in the output signal of the interrogation device by means of which it is possible to check the presence and the correctness of the inserted key.
U.S. Pat. No. 4,486,806 to Mochida et al. (European patent EP 0 065 650 B1) discloses an electronic door locking system for motor vehicles. There, the position of the ignition lock, and thus the position of the ignition key, is interrogated and the door lock system is controlled as a function of the position of the ignition key. Furthermore, Mochida et al. teach how to determine whether the ignition key is still in the ignition lock and, if this is the case, to disable the generation of a door locking signal. In all these cases it is necessary to detect whether or not the key is inserted into the lock.
It is accordingly an object of the invention to provide a device for detecting a key which has been inserted into a motor vehicle lock, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which permits quick and reliable key detection with little expenditure and provides for a high degree of reliability.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for detecting a key inserted into a lock of a motor vehicle, wherein, when the key is inserted in the lock, the key communicates via a communications link with a lock-end interrogation device emitting intermittent interrogation pulses, the device which comprises:
a microprocessor, a transmitter connected to the microprocessor, and a receiver connected to the microprocessor; and
a circuit arrangement connected directly between the transmitter and the receiver and bypassing the microprocessor, the receiver activating the circuit arrangement upon receiving an interrogation pulse and actuating the transmitter to transmit a response pulse in response to the interrogation pulse.
The receiver and the transmitter of the key are connected to one another directly via a circuit arrangement which, when the interrogation pulse is received, can activate the transmitter immediately or else with a time delay, in order to generate the response pulse. The outputting of the response pulse is thus implemented purely by means of circuitry so that the reaction time of the key is very short, that is to say the response pulse is generated very quickly, and the current consumption of the key still remains low. The generation of the response pulse thus requires no software support so that the microprocessor in the key can remain in the stand-by mode (power-down mode) during this interrogation xe2x80x9cis key inserted?xe2x80x9d. The energy requirement is thus minimized.
The interrogation pulses are emitted intermittently, i.e. at regular or irregular time intervals, by the lock-end interrogation device, i.e. the interrogation device in the motor vehicle, and are replied to with short response pulses by the key inserted in the lock, said pulses being preferably transmitted via the communications link, for example an infrared link, a radio link of a remote-control system which may be in the key or of a communications link of inductive design, and being evaluated in the interrogation device, that is to say in the evaluating logic which is in the motor vehicle, as an indication that the key is inserted.
In the embodiment according to the invention there is thus no need for an additional sensor such as a mechanical push button switch, a Reed contact, a Hall sensor, a photoelectric barrier etc. The inserted state of the key is sensed via the functional components which are already provided in the system for other purposes.
The intermittent interrogation may take place cyclically, for example at time intervals of 50 ms or greater, so that there is no appreciable increase in the quiescent current of the interrogation device and the interrogation device can also remain permanently activated even when the ignition is switched off. Since the interrogation takes place very quickly, the insertion of a key into the ignition lock can be detected very rapidly so that no significant system delay times occur.
In accordance with an added feature of the invention, the circuit arrangement is adapted to time an end of the response pulse to lie after a trailing edge of the interrogation pulse. In other words, the end of the response pulse is delayed in relation to the end of the interrogation pulse so that the interrogation device (evaluation logic) can distinguish the response pulse clearly from interference signals which are generated by reflections or other influences of the interrogation pulse, but drop away immediately to zero at the end of the interrogation pulse.
For this purpose, the circuit arrangement may contain a timing element which delays the switching off of the response pulse so that the response pulse persists for a certain time period after the interrogation pulse has already ended.
The key may be provided with a battery, implemented for example as an accumulator, which makes available the energy necessary for outputting the response pulse and also ensures the energy supply for the further components contained in the key, for example the microprocessor. Alternatively, the energy necessary for outputting the response pulse may also be drawn by the key by means of inductive supply from the interrogation device, for example the evaluating control unit. For this purpose, the key then preferably has an LC oscillatory circuit with energy accumulator connected downstream.
In accordance with an additional feature of the invention, the receiver is an infrared receiver or an inductive antenna, and the transmitter is an infrared transmitter or a radio-frequency transmitter.
In accordance with another feature of the invention, the circuit arrangement is a timing elementxe2x80x94such as an RC elementxe2x80x94adapted to delay a switching off of the response pulse in relation to a trailing edge of the interrogation pulse.
In accordance with a further feature of the invention, the receiver includes an LC oscillatory circuit, and including an energy accumulator connected to and chargeable by the LC oscillatory circuit, and wherein the circuit arrangement is adapted to respond to an interrogation pulse sensed by the LC oscillatory circuit and to generate a response pulse in reaction thereto.
As noted above, the transmitter and receiver of the key may be designed as infrared transmitters or infrared receivers, the interrogation device (evaluation logic of the motor vehicle) being likewise provided with an infrared transmitter for generating the interrogation pulses and with an infrared receiver for acquiring the response pulses. The infrared link is designed here preferably as a bidirectional infrared link via which not only the interrogation and response pulses but also, if appropriate, additional information can be exchanged between the key and the motor vehicle. Alternatively, the communications link may also be designed as a radio link, the key and the evaluation logic being equipped with appropriate RF transmitters and RF receivers. Here, the appropriate pulses may be exchanged by means of inductive antennas of the key and/or of the interrogation device. The radio link of a remote-control system which may be in the key, or an inductive link, may thus be used to generate the response pulses.
In accordance with an alternative feature of the invention, the receiver includes an inductive input circuit, and including an interrogation device containing an inductive output circuit, and wherein the response pulses generated by the transmitter consist in a change in a load resistance over time, leading to corresponding change in a detuning of the inductive output circuit of the interrogation device caused by the detuning of the inductive input circuit of the key. In other words, if the interrogation device is equipped with an inductive output circuit, and the key contains an inductive input circuit, the response pulse generated by the key may also merely take the form of the detuning which occurs in the inductive output circuit of the interrogation device (for example control unit) in the presence of the inductive load of the input oscillatory circuit of the key. The interrogation device can sense and evaluate this detuning as a clear indication of the presence of the key. The xe2x80x9cresponse pulsesxe2x80x9d consist, in this case, in the change in the energy of the field over time which is brought about by the inductive input circuit of the key in comparison with the situation in which the key is not inserted. The inductive output circuit of the interrogation device and the inductive input circuit of the key are provided here for the wireless energy supply and do not constitute additionally necessary components.
In accordance with again a further feature of the invention, the load resistance changes at a specific frequency or in accordance with a coded item of information.
So that the presence of the key can be detected even more reliably, the key preferably changes its load resistance over time, for example with a specific frequency or in accordance with a specific item of coded information. This change in the load resistance can be effected, for example, by cyclically short-circuiting or switching off inductive sections of the inductor in the input circuit or else in some other way. These load changes which take place with a specific frequency or according to a predefined pattern lead to corresponding changes in the detuning, in the form of a corresponding, superimposed modulation, in the evaluation logic. The presence of this superimposed modulation provides for the evaluation logic the clear information that the key is now inserted and that there are, for example, no interference effects or other inductive loads.
With the above and other objects in view there is also provided, in accordance with the invention, a key for a motor vehicle with a system for detecting whether the key is inserted in a lock of the motor vehicle, comprising:
a receiver for sensing externally fed-in signals, a microprocessor and a transmitter for transmitting signals to an outside of the key;
a circuit arrangement connected directly between the transmitter and the receiver and bypassing the microprocessor, the circuit arrangement controlling the transmitter to generate a response pulse when an interrogation pulse is received by the receiver.
In accordance with again an additional feature of the invention, the circuit arrangement includes a timing element for delaying a trailing edge of the response signal relative to a trailing edge of a received signal.
In accordance with again an alternative feature of the invention, the circuit arrangement responds to a trailing edge of a received signal and generates a response pulse in reaction thereto.
In accordance with a concomitant feature of the invention, there is provided, in combination with a motor vehicle and a key for the motor vehicle, a device for detecting whether the key is inserted into a lock of the motor vehicle, such as the ignition lock. The system comprises:
a communications link between the key and the motor vehicle whereby, when the key is inserted in the lock, the key communicates via the communications link with a lock-end interrogation device emitting intermittent interrogation pulses;
a microprocessor, a transmitter connected to the microprocessor, and a receiver connected to the microprocessor; and
a circuit arrangement connected directly between the transmitter and the receiver and bypassing the microprocessor, the receiver activating the circuit arrangement upon receiving an interrogation pulse from the lock-end interrogation device and actuating the transmitter to transmit a response pulse to the interrogation device in response to the interrogation pulse.
The invention is preferably used for detecting the inserted state of the ignition key into the ignition lock of a motor vehicle, but can also be used in the case of a door lock for sensing the insertion of the motor vehicle key.
The invention can be used in electronic keys with inductive energy supply, for example with transponder systems or with remote-control systems which are based on radio or infrared, in which case a bidirectional radio-frequency or infrared interface with the interrogation device (control unit), for example of an electronic ignition system, may also be provided.
The invention may alternatively or additionally also be used for controlling an immobilizer of the motor vehicle which is activated as soon as the interrogation device determines that the ignition key has been withdrawn (and, if appropriate, further preconditions are also fulfilled), and which can be activated only if one or more correct response pulses have been obtained, that is to say the ignition key has been inserted again.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for detecting a key inserted in a motor vehicle lock, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.